Recently, to make a smaller and highly functionalized electronic system, heat generating elements are concentrated therein, and thus a method of efficiently cooling the elements is required. In addition, there is a demand for a method of effectively controlling heat generated from a secondary battery while an electric vehicle is driven using the secondary battery as a power source.
Generally, heat generated from electronic systems or secondary batteries is dissipated into the air, and a general heat dissipating method is mainly performed using a heat dissipation device manufactured of a metal with excellent thermal conductivity such as aluminum or copper. However, such a method cannot ensure electrical insulation, and thus a separate device such as a fuse is needed, and due to the properties of the metal, the device generally becomes heavy.
To overcome such a disadvantage, a method of preparing a composite material by dispersing inorganic particles having high thermal conductivity into a resin formed in a matrix, for example, a silicon-based resin or an epoxy-based resin.
In terms of a material for a thermally conductive filler in the thermally conductive polymer composite material, metal particles are effective in improving thermal conductivity, but do not have electrical insulation and thus are not conventionally used as a thermally conductive filler. Mostly, among metal oxides and metal nitrides, one that has excellent thermal conductivity and electrical insulation has been used as the thermally conductive filler.
To obtain the high thermal conductivity, a composite material is prepared by dispersing a considerable amount of thermally conductive filler into an epoxy- or silicon-based resin. However, according to the above-described method, first, a cost is increased, and second, viscosity is sharply increased and a mechanical property and a molding property are sharply decreased, and therefore it is difficult to actually take advantage of a thermally conductive polymer composite material. Accordingly, to ensure mobility for injection molding and optimum levels of physical properties, the current development of the thermally conductive polymer composite material is progressing to obtain optimal thermal conductivity with the minimum content of the thermally conductive filler.
To obtain the optimal thermal conductivity with the minimum content of the thermally conductive filler, phonon-scattering occurring in heat transfer has to be minimized. In addition, a thermal pathway in which thermally conductive fillers are in direct contact with each other in a polymer matrix has to be formed, and specifically, the thermally conductive fillers have to be arranged in desired positions.
However, it is difficult to construct sufficient thermal pathways by a conventional technique of preparing a thermally conductive ceramic-polymer composite material, for example, simply mixing a thermally conductive ceramic and a liquid polymer or polymer powder.
Therefore, to obtain the optimal thermal conductivity with the minimum content of the thermally conductive filler, it is necessary to develop the thermally conductive polymer composite material in which the thermal pathway of the thermally conductive fillers in the polymer matrix of the composite material is formed, and which uses a method of forming chemical bonds at the interface between the ceramic filler and the polymer matrix.